1. Field of the Invention
This invention relates to a head deviation measurement method, a data recording/reproducing method, a head deviation measurement apparatus and a data recording/reproducing apparatus. For example, it relates to a magnetic disc apparatus on which a recording head for recording data on a magnetic disc and a playback head for reproducing data from the magnetic disc are provided separately from each other.
2. Description of the Related Art
In a magnetic disc apparatus for recording data on a disc-shaped recording medium, such as a magnetic disc, or reproducing data from a magnetic disc, a so-called magneto-reluctance type head (MR head) is used as a playback head for raising the playback sensitivity. In this type of the magnetic disc apparatus, that is a magnetic disc apparatus provided with an induction type (ind type) recording head and an MR type playback head, the playback head is designed so as to have a width narrower than that of the recording head, that is the width of the playback head is reduced as compared to the width of the track formed by the recording head scanning the magnetic disc, so that no operating hindrances will be caused even if the magnetic disc apparatus is produced with the center of the recording head deviated from the center of the playback head such that the center of the playback head is deviated from the center of the track formed by the recording head.
However, this method has a drawback that the width of the recording head needs to be designed with an allowance to a broader width, such that it is not possible to raise the recording density.
There is also known such a magnetic disc apparatus in which the recording head is designed to have a width approximately equal to the width of the playback head and the deviation between the center of the recording head and that of the playback head are optically measured in the head producing process using, for example, a microscope, this deviation being then sent as a correction amount (termed offset) to a positioning servo (so-called tracking servo) circuit so as to be summed to or subtracted from a positioning error signal (so-called tracking error signal) representing the position deviation in order to correct the tracking position of the recording head or the playback head and in order to eliminate the designing allowance referred to above for realizing a high recording density. However, the deviation between the center of the recording head and that of the playback head is time-consuming and costly, while the above method cannot cope with transmutations with lapse of time.